This application generally relates to olefin polymerization catalyst compositions and olefin polymerization processes using the same.
The use of late transition metal complexes as catalysts for olefin polymerization has recently been reviewed by Ittel et al. (Chem. Rev. 2000, 100, 1169). Late transition metal catalysts have also been described in WO 01/07492, WO 01/55231, WO 01/42257, WO 01/21586, and Organometallics 2001, 20, 2321. Notwithstanding the developments described therein, there remains a need for new late transition metal catalysts and processes with improved productivities under commercial reactor operating conditions, especially those involving gas phase processes. New catalysts and processes for these purposes are described herein.
Gas phase processes represent a large fraction of current worldwide polyethylene production, and generally involve the use of hydrogen to control the polymer molecular weight. Although many nickel catalysts are severely inhibited by added hydrogen, we have previously described, in U.S. patent application Ser. No. 09/507,492, filed Feb. 18, 2000, U.S. patent application Ser. No. 09/563,812, filed May 3, 2000, and U.S. patent application Ser. No. 09/231,920, filed Sep. 11, 2000, preferred classes of nickel catalysts that exhibit little or no loss of catalytic activity in homogeneously initiated, solution or slurry phase reactions conducted in the presence of hydrogen. We have, however, unexpectedly observed that these same, otherwise hydrogen-tolerant catalysts frequently exhibit an inappropriate response to hydrogen in supported catalyst gas phase polymerizations, in that much poorer productivities are observed when ethylene polymerizations are carried out in the presence of hydrogen, compared to similar reactions without hydrogen. In an effort to solve this problem, we have surprisingly discovered that treating the support with a pore-filling agent, either before, during, or after the catalyst and the support have been combined, can significantly improve the catalyst productivity in the presence of hydrogen. Pore-filling agents suitable for use in the present invention include materials that are: (a) compatible with the desired catalysis, by which we mean the pore-filling agent either does not interfere with the desired catalysis, or acts to usefully modify the catalyst activity or selectivity, and (b) (i) low in volatility, by which we mean the pore-filling agent is either sufficiently non-volatile that not all of it is lost before the catalyst is introduced into the olefin polymerization reactor and olefin polymerization is initiated, and enough remains to improve the catalyst productivity in the presence of hydrogen, or (ii) relatively more volatile, but the treated supported catalyst can be handled in such a way that a sufficient amount of the pore-filling agent remains when the supported catalyst is exposed to hydrogen that improved productivity is observed in the presence of hydrogen. Examples of such pore-filling agents include, but are not limited to, triethylborane, diethylzinc, triethylaluminum, xylene, and triphenylmethane.
We have also discovered that activating supported Group 8-10 metal catalysts in the presence of one or more olefins, but in the absence of hydrogen, can also result in significantly improved productivities upon subsequent exposure to hydrogen. We have further discovered that improved productivities in the presence of hydrogen can also be achieved by activating the supported Group 8-10 metal catalysts at high partial pressures of ethylene. By xe2x80x9chigh partial pressures of ethylenexe2x80x9d, we mean partial pressures of at least 400 psig, preferably at least 600 psig.
These discoveries are both surprising and unexpected because the art did not teach either the problem of decreased productivity of supported catalysts based on cationic nickel complexes of bidentate ligands that are exposed to hydrogen during gas phase polymerization or a solution to the problem, e.g., the use of certain pore-filling agents, the controlled exposure to hydrogen, or the control of the ethylene partial pressure during catalyst activation.
Although it is recognized that the above-mentioned treatment of the support may result in both chemical and physical modifications of the supported catalysts, we believe, without wishing to be bound by theory, that the pore-filling agent may be acting to affect the relative concentrations of key reactants at the site of the Group 8-10 metal catalyst during activation, either by acting as a physical barrier to diffusion or by virtue of the different solubilities of the key reagents in the pore-filling agent. In particular, we believe that the pore-filling agent acts to raise the relative concentration of ethylene to hydrogen at the active site at the time of activation. Activating the catalyst in the presence of olefin, but in the absence of hydrogen, may result in a similar effect wherein the polymer itself serves to modify the relative concentrations of key reagents. In addition to the concentration of hydrogen and olefin, the concentration of the co-catalyst(s) and the concentration of the catalyst itself may also be usefully modified through the use of the specified pore-filling agents. Activating the catalyst in the presence of hydrogen at relatively high partial pressures of ethylene may also result in improved catalyst productivity in the presence of hydrogen for the same reason. Without wishing to be bound by theory, we believe that it is important that the activated catalyst react with ethylene or another olefin before it reacts with hydrogen.
Thus, in a first aspect, this invention pertains to an improved process for the polymerization of olefins, comprising: contacting one or more olefins with a catalyst comprising a Group 8-10 transition metal complex of a bidentate N,Nxe2x80x94, N,Oxe2x80x94, N,Pxe2x80x94, or P,P-donor ligand, wherein the catalyst is attached to a solid support, wherein the solid support has been treated with a pore-filling agent, either before, during, or after the catalyst and the support have been combined, wherein the pore-filling agent is introduced into the pores of the support either as a pure liquid or as a solution in a suitable solvent. By xe2x80x9csuitable solventxe2x80x9d, we mean a solvent that (a) is itself a useful supported catalyst pore-filling agent, (b) is readily removed prior to polymerization, or (c) is compatible with the process and does not inhibit the catalyst, unless any such inhibition is modest and advantageous in the context of the process, as would be the case, for example, if the catalyst activated more slowly and thereby reduce a tendency for particle overheating in a gas phase reactor. Such overheating can lead to particle agglomeration and reactor fouling.
In a first preferred embodiment, the ligand is selected from Set 1; 
wherein:
R2x,y are each independently H, hydrocarbyl, substituted hydrocarbyl, heteroatom connected hydrocarbyl, heteroatom connected substituted hydrocarbyl, silyl, or ferrocenyl; in addition, R2x and R2y may be linked by a bridging group;
R3a-l are each independently H, hydrocarbyl, substituted hydrocarbyl, heteroatom connected hydrocarbyl, heteroatom connected substituted hydrocarbyl, fluoroalkyl, silyl, boryl, fluoro, chloro, bromo, cyano, or nitro; and
R4a,b are each independently hydrocarbyl, substituted hydrocarbyl, heteroatom connected hydrocarbyl, or heteroatom connected substituted hydrocarbyl; in addition, R4a and R4b may be linked by a bridging group.
In a second preferred embodiment, the catalyst comprises a nickel complex of a bidentate N,N-donor ligand, wherein the N-donor atoms are substituted by aromatic or heteroaromatic rings, wherein the ortho positions of the rings are substituted by bromo, trifluoromethyl, fluoroalkyl, aryl, or heteroaryl groups.
In a third preferred embodiment, at least 20%, more preferably at least 40%, even more preferably at least 60%, of the remaining pore volume of the supported catalyst is filled by the pore-filling agent. By xe2x80x9cremaining pore volumexe2x80x9d, we mean the pore volume of the support minus the volume occupied by the catalyst and any co-catalyst.
In a second aspect, this invention relates to a process for the polymerization of olefins, comprising: contacting one or more olefins with a catalyst comprising a Group 8-10 transition metal complex of a bidentate N,Nxe2x80x94, N,Oxe2x80x94, N,Pxe2x80x94, or P,P-donor, wherein the catalyst is attached to a solid support and wherein the catalyst is first activated in the absence of hydrogen in a first reactor containing one or more olefins, and then introduced into a second reactor containing hydrogen in which the bulk of the polymerization takes place.
In a first preferred embodiment of this second aspect, the process comprises a nickel complex of a bidentate N,N-donor ligand, wherein the N-donor atoms are substituted by aromatic or heteroaromatic rings, wherein the ortho positions of the rings are substituted by bromo, trifluoromethyl, fluoroalkyl, aryl, or heteroaryl groups.
In a second preferred embodiment of this second aspect, the ligand is selected from Set 2;
wherein:
R2x,y are each independently H, hydrocarbyl, substituted hydrocarbyl, heteroatom connected hydrocarbyl, heteroatom connected substituted hydrocarbyl, silyl, or ferrocenyl; in addition, R2x and R2y may be linked by a bridging group;
R3a-l are each independently H, hydrocarbyl, substituted hydrocarbyl, heteroatom connected hydrocarbyl, heteroatom connected substituted hydrocarbyl, fluoroalkyl, silyl, boryl, fluoro, chloro, bromo, cyano, or nitro; and
R4a,b are each independently hydrocarbyl, substituted hydrocarbyl, heteroatom connected hydrocarbyl, or heteroatom connected substituted hydrocarbyl; in addition, R4a and R4b may be linked by a bridging group.
In a fourth preferred embodiment of this second aspect, two or three of the ortho positions of the rings are substituted by aryl or heteroaryl groups, and the remainder of the ortho positions are substituted by bromo, trifluoromethyl, or fluoroalkyl groups.
In a third aspect, this invention relates to a process for the polymerization of olefins, comprising: contacting one or more olefins with a catalyst comprising a Group 8-10 transition metal complex of a bidentate N,Nxe2x80x94, N,Oxe2x80x94, N,Pxe2x80x94, or P,P-donor, wherein the catalyst is attached to a solid support, and wherein the catalyst is first activated in the presence of hydrogen at a partial pressure of ethylene greater than 400 psig.
In a first preferred embodiment of this third aspect, the partial pressure of ethylene is at least 600 psig.